A blotchy mole, a burning belly, bleeding gums. They're all unpleasant things to experience, but hardly dangerous. At least that's what many of us think.

Yet if these and other everyday ailments linger too long, they could be a sign that something much more serious is going on. Here are six symptoms people often wish they had checked out sooner.

1. A Burning Stomach. Pain used to pierce Darlene Essick, 51, from her stomach through her back unless she took an antacid every 90 minutes. "It got so bad I could hardly eat," recalls the mother of three from Minerva, Ohio. "I was down to 97 pounds."

In 1995, doctors diagnosed an ulcer, a condition that 20 million Americans will suffer at least once in their lifetime. An ulcer is a break in the lining of the stomach or top part of the intestine. Most are cured without further complications, but a few rare ulcers can develop into potential life-threatening conditions.

Darlene's ulcer was caused by aspirin she regularly took for arthritis. The ulcer went away after she stopped taking aspirin and began taking acid reducers.

Prevention: "Stress, alcohol, and diet have nothing to do with ulcers," says Dr. Gary Falk, a staff gastroenterologist at the Cleveland Clinic. Limiting intake of nonsteroidal anti-inflammatory drugs such as aspirin, Motrin, Nuprin, and Advil helps, says Dr. Falk. "Just because they're over-the-counter doesn't mean they're perfectly safe." In fact, one of the most common causes of internal bleeding is the consumption of these medicines.

Tests: Doctors commonly diagnose ulcers one of two ways: A barium X ray, which requires a patient to drink a chalky iodine mixture that outlines the gastrointestinal tract; or an upper endoscopy, which requires a tube down the esophagus so the doctor can look at the stomach through a tiny telescope. A blood or breath test also can reveal the presence of Helicobacter pylori, a bacteria present in about 90 percent of ulcers.

Treatment: A daily dose of Zantac, Tagamet, Prilosec, or Prevacid will reduce stomach acid, and antibiotics help fight Helicobacter pylori.

For more information: Talk to your doctor.

2. Blood in Your Stool. When Anna Kessler of Middleburg Heights, Ohio, first spotted blood in her stool, she thought it was probably just hemorrhoids. "Then the doctor dropped a bomb on me: colon cancer," she says. "I was shocked. I was the picture of health -- and I was only forty. I said, 'Aren't I supposed to be sick?'"

Not necessarily.

Colon cancer -- an uncontrolled growth of cells in the large intestine -- often strikes with few clues, says Dr. James Church, staff colorectal surgeon at The Cleveland Clinic. This year, more than 150,000 people will be diagnosed with colon cancer and 57,700 people will die from it. Most colon cancer patients are diagnosed with this disease in their 60s; yet, a recent report by the Centers for Disease Control says that less than one-third of older Americans have been screened for it. The reasons given for not being tested were embarrassment, cost, and doctors who never mentioned the test.

Anna, now 42, was one of the lucky ones. A month after her diagnosis, doctors removed 1-1/2 feet of her colon as well as all signs of the cancer. "The greatest night was February 24, 1997, when the surgeon said that though I probably had the cancer for five years, it hadn't spread."

Colon cancer symptoms: Symptoms depend on the location and extent of the cancer, but common signs are fatigue, constipation alternating with frequent bowel movements, diarrhea, or weight loss. Sometimes there is abdominal pain and rectal bleeding.

Prevention: Everyone should have an annual digital rectal exam beginning at age 40 and an annual test for blood in the stool starting at age 50. Also, every three to five years, starting at 50, you should get a flexible sigmoidoscopy. This is done with a slender, lighted tube slipped into the rectum, allowing the doctor to look for cancer or polyps (small growths that can become cancerous). People with an inflammatory bowel disease or family history of colorectal cancer should consult their doctor about earlier and more frequent screenings, says Dr. Robert C. Kurtz, a gastroenterologist at Memorial Sloan-Kettering Cancer Center and professor of medicine at Cornell University Medical College. These patients also should request a colonoscopy, in which a lighted tube with a tiny video camera is inserted through the rectum so the doctor can view the entire colon. Regular exercise and quitting smoking are also helpful. An ideal daily diet includes 25 grams of fiber, five servings of fruit and vegetables, little red meat, and less than 20 percent fat.

Treatment: The cancerous area, and often surrounding lymph nodes, is removed and the remaining colon reconnected. Radiation and chemotherapy also may be needed.

For more information: Contact the American Cancer Society (800/227-2345).

3. Lack of Energy/General Ill Feeling. Thyroid symptoms are so vague that doctors easily misdiagnose them. Sally Templeton, a nurse in Houston, never even suspected her thyroid might be the cause when she began feeling bad. "I thought I had a circulatory problem or was getting diabetes," says Sally, 34. She was exhausted, constipated, gaining weight, and having heavy menstrual cycles. "At times my hands and feet were like sheets of ice and nobody else was cold."

During a physical four years ago, a blood test showed her thyroid was producing too little thyroid hormone, a condition called hypothyroidism. The thyroid gland makes a hormone that regulates the body's metabolism, telling the body how fast to work and use energy.

More than 7 million Americans have an underactive thyroid or an overactive one, called hyperthyroidism. This often occurs when the body's autoimmune system turns against the thyroid gland, inflaming it and stimulating it to produce too much hormone. It leads to headaches, weight loss, and muscle weakness.

Thyroid symptoms: For an underactive thyroid, the range of signs includes dry skin, impaired memory and concentration, depression, a husky voice, and thinning hair. Signs of an overactive thyroid include trembling hands, a racing heart, light menstrual periods, hair loss, an orange-peel-like thickening of the skin over the shins, or an enlarged thyroid gland.

Prevention: None.

Tests: A blood test determines the amount of Thyroid Stimulating Hormone. The normal level is .4 to 5.5.